In enzymology, a geissoschizine dehydrogenase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are geissoschizine and NADP<sup>+</sup>, whereas its two products are 4,21-didehydrogeissoschizine and NADPH.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is geissoschizine:NADP+ 4,21-oxidoreductase. This enzyme participates in indole and ipecac alkaloid biosynthesis.